1. Field of the Invention
The present invention relates to a joined body, a method for manufacturing the same and particularly relates to a high pressure discharge lamp.
2. Description of the Related Art
A high pressure discharge lamp has a ceramic discharge tube with two end portions, in which sealing members (usually referred to as a ceramic plug) are inserted, respectively, to seal the respective end portions. A through hole is formed in each sealing member and a metal member, to which a predetermined electrode system is attached, is inserted within the through hole. An ionizable light-emitting material is introduced and sealed within the inner space of the discharge tube. Known high pressure discharge lamp includes a high pressure sodium vapor and metal halide lamps, the latter exhibiting more superior color coordination. The lamp may be used in high temperature condition by forming the discharge tube by a ceramic material.
In such discharge lamps, it is necessary to provide an air-tight seal between the end portion of the ceramic discharge tube and a member for supporting an electrode system. The ceramic discharge tube has a main body with a shape of a tube with two narrow ends, or a barrel, or a straight tube. The ceramic discharge tube is made of, for example, an alumina sintered body. The end portion of the ceramic discharge tube may be sealed, for example, by the following method disclosed in Japanese patent publication Kokai (Tokkaihei) 318,435/1994. A sealing member is inserted and supported in the end portion of the ceramic discharge tube. A through hole is formed in the longitudinal direction of the center axis of the sealing member. An elongate member for supporting an electrode system is inserted and fixed within the through hole. The sealing member is made of a cermet containing both of alumina and a metal constituting the member for supporting an electrode system in a predetermined ratio, so that the sealing member has a thermal coefficient between those of the electrode-system supporting member and ceramic discharge tube.
When producing such a sealing structure, the calcined bodies of the ceramic discharge tube and sealing member are designed so that the end portion of the discharge tube has an inner diameter smaller than that of the outer diameter of the sealing member, when the calcined bodies are sintered without inserting the calcined body of the sealing member within the end portion of the calcined body of the tube. Therefore, the sealing member is tightly clamped and held in the end portion of the ceramic discharge tube. The sealing member and the electrode system supporting member are similarly designed.
However, the inventor further examined the above sealing structure and found the following problems. That is, in this sealing structure, the sealing member and the electrode-system supporting member are sealed with each other by a pressure applied between them. However, considering that many and repeated cycles of turning-on and turning-off are applied on the structure and the difference of the thermal expansion coefficients thereof, it is necessary to further improve the reliability of the sealing structure. In particular, it is necessary to develop a sealing structure with high corrosion resistance and improved reliability when using a metal halide being highly corrosive.
That is, it is necessary to provide a joined structure, in which a ceramic discharge tube or a sealing member, for example made of alumina, and a metal member, for example made of molybdenum, may be joined with a high strength, the resulting joined structure has improved air-tightness and resistance to corrosion, and repeated cycles of turning-on and turning-off does not result in the fracture of the joined structure. Moreover, the sealing member may be made of a cermet. In such a case, the above properties are demanded for the joined structure of the sealing and metal members.
It is an object of the invention to provide a joined structure of a ceramic member or a cermet member and a member made of a metal such as molybdenum, in which the members may be joined with a high strength, the joined structure has improved air-tightness and resistance to corrosion and repeated thermal cycles does not result in the fracture of the joined structure, and to provide a method for manufacturing the same.
It is another object of the invention to apply such joined structure to a high pressure discharge lamp, for improving the resistance to a corrosive gas, such as a metal halide, improving the air-tightness, and for avoiding the fracture of the joined structure due to repeated cycles of turning-on and turning-off.
The present invention provides a joined body of a first member made of a metal and a second member made of a ceramics or a cermet, the joined body comprising a joining portion interposed between the first member and the second member for joining the first and second members, wherein the joining portion comprises main phase contacting the first member and an intermediate glass layer contacting the second member and existing between the second member and the main phase, the main phase being composed of a porous bone structure, with open pores and made of a sintered product of metal powder, and a glass phase impregnated into the open pores in the porous bone structure.
The present invention further provides a ceramic discharge lamp comprising a ceramic discharge tube with an inner space formed therein and end portions, the inner space being filled with an ionizable light-emitting material and a starter gas and an opening being formed within the end portion, an electrode system provided within the inner space, a sealing member with a through hole formed therein, a part of the sealing member being fixed within the opening of the ceramic discharge tube, and a metal member, wherein the metal member and the sealing member constitute the above air-tight joined body with the metal member being the first member and the sealing member being the second member.
The present invention further provides a ceramic discharge lamp comprising a ceramic discharge tube with an inner space formed therein and end portions, the inner space being filled with an ionizable light-emitting material and a starter gas and an opening being formed within the end portion, an electrode system provided within the inner space and a metal member, wherein the metal member and the ceramic discharge tube constitute the above air-tight joined body with the metal member being the first member and the ceramic discharge tube being the second member.
The invention further provides a method for manufacturing a joined body of a-first member made of a metal and-a second member made of a ceramics or a cermet, the method comprising the steps of: providing a porous bone structure, with open pores and made of a sintered product of metal powder, between the first member and the second member, and impregnating a glass, melted at a temperature lower than the melting point of the metal constituting the porous bone structure, into the open pores of the porous bone structure to produce a main phase composed of the porous bone structure and a glass phase made of the glass impregnated into the open pores, and to flow the melted glass between the second member and the main phase to produce a intermediate glass layer, so that the first member and second member is joined.